Friction and wear properties of rice husk ceramics under dry condition

The friction and wear behaviors of rice husk (RH) ceramics, prepared by carbonizing the mixture of rice husk and phenol resin at 900 °C in N₂ gas environment, sliding against high carbon chromium steel (JIS SUJ2), austenitic stainless steel (JIS SUS304), and Al₂O₃ under dry condition were investigated using a ball-on-disk tribometer. The test results show that the friction coefficient of RH ceramics takes very low values 0.05–0.08 and 0.06–0.11 sliding against SUJ2 and SUS304, respectively, and much higher values around 0.14–0.23 against Al₂O₃. It was also shown that SUJ2 provides the lowest specific wear rate values below 10⁻⁹ mm²/N, while, those of SUS304 and Al₂O₃ mostly stayed between 10⁻⁹ to 10⁻⁸ mm²/N range. The worn surfaces of counterparts were observed with optical microscopy and analyzed using cross-sectional transmission electron microscopy with energy dispersive X-ray spectroscopy and electron diffraction. It was suggested that the tribological behaviors of RH ceramics are closely related with the formation of a transferred film, consisted of amorphous silica and carbon particles, on a counterpart surface. The transferred film was formed readily on SUJ2 balls, whereas for SUS304 the presence of the film was subject of the sliding conditions. Moreover, formation of the transferred film could not be detected on Al₂O₃ counterparts.     

Dry and oil-lubricated sliding wear of Si<Subscript>3</Subscript>N<Subscript>4</Subscript> and Si<Subscript>3</Subscript>N<Subscript>4</Subscript>/BN fibrous monoliths

A high-temperature ball-on-flat tribometer was used to investigate dry and oil-lubricated friction and wear of sintered Si₃N₄ and Si₃N₄/hexagonal boron nitride (H-BN) fibrous monoliths. The friction coefficients of base Si₃N₄ flats sliding against Si₃N₄ balls were in the range of 0.6–0.8 for dry and 0.03–0.15 for lubricated sliding, and the average wear rates of Si₃N₄ were 10^–5 mm³ N^–1 m^–1 for dry sliding and 10^–10–10^–8 mm³ N ^–1m^–1 for lubricated sliding. The friction coefficients of Si₃N₄ balls against composite fibrous monoliths were 0.7 for dry sliding and 0.01–0.08 for lubricated sliding. The average specific wear rates of the pairs were of the same order as those measured for the conventional Si₃N₄ pairs. However, the fibrous monoliths, in combination with sprayed dry boron nitride, resulted in reduction in the lubricated friction coefficients of the test pairs and significant reduction in their wear rates. The most striking result of this study was that the coefficients of friction of the Si₃N₄/H-BN fibrous monolith test pair were 70–80 lower than those of either roughened or polished Si₃N₄ when tests were performed under oil-lubricated sliding conditions over long distances (up to 5000 m). The results indicated that Si₃N₄/H-BN fibrous monoliths have good wear resistance and can be used to reduce friction under lubricated sliding conditions.     

Ionic Liquid Lubrication Effects on Ceramics in a Water Environment

Ionic liquids were studied to determine their effectiveness as boundary lubricant additives for water. The chemical and tribochemical reactions that govern their behavior were probed to understand lubrication mechanisms. Under water lubricated conditions, silicon nitride ceramics are characterized by a running-in period of high friction, during which time the surface is modified causing a dramatic decrease in friction and wear. Two mechanisms have been proposed to explain the friction and wear behavior. Si₃N₄ sliding against itself may result in tribochemical reactions that form a hydrated silicon oxide layer on the surface of the sliding contact. This film has been suggested to mediate friction and wear. Others have suggested that tribo-dissolution of SiO₂ results in an ultra smooth surface and after a running-in period of high wear, the lubrication mode becomes hydrodynamic. The goal of this study was to examine the effects that ionic liquids have on the friction and wear properties of Si₃N₄, in particular their effects on the running-in period. Tribological properties were evaluated using pin-on-disk and reciprocating tribometers. The tribological conditions of the tests were selected to produce mixed/hydrodynamic lubrication. The relative lubrication mode between mixed and hydrodynamic was controlled by the initial surface roughness. Solutions containing 2 wt% ionic liquids were produced for testing purposes. Chemical analysis of the sliding surfaces was accomplished with X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The test specimens were 1 in diameter Si₃N₄ disks sliding against 1/4 in Si₃N₄ balls. The addition of ionic liquids to water resulted in dramatically reduced running-in periods for silicon nitride from thousands to the hundreds of cycles. Proposed mechanisms include the formation of BF_x and PF_x films on the surface and creation of an electric double layer of ionic liquid.     

Wear of aligned silicon nitride under dry sliding conditions

The wear behaviour of textured silicon nitride (Si₃N₄) ceramics with aligned microstructures was analyzed under abrasive wear conditions. Dry reciprocating self-mated ball-on-flat wear tests were performed to study the influence of different microstructural plane/orientation combinations on the Si₃N₄ tribological behaviour. Textured materials showed superior wear resistance than non-textured reference Si₃N₄ for the whole range of loads and contact pressures, 5–50 N and 1.7–3.6 GPa, respectively, with an increase of about 70% for the maximum applied load. Within textured materials, the plane perpendicular to the extruding direction exhibited a 50% higher wear resistance (4 × 10^?5 mm³ N^?1 m^?1) than the parallel plane where the elongated grains were aligned. The severe wear process involved debonding, fracture and debris formation mechanisms. The progress of this sequence depended on the particular microstructure of each plane/orientation combination. A relationship between abrasive wear resistance and selected microstructural parameters has been established.     

Friction Reduction and Wear Resistance Enhancement of SiC and Si3N4 Ceramics under Dry Conditions

In this study, an effort was made to control the friction and wear behavior of silicon carbide (SiC) and silicon nitride (Si₃N₄) ceramics using an ultrasonic nanocrystalline surface modification (UNSM) technique. The friction and wear behavior of the ceramic specimens was investigated using a ball-on-disk tribotester under dry conditions against two different Si₃N₄ and bearing steel (SUJ2) balls. The experimental test results revealed the possibility of controlling the friction and wear behavior of ceramics, where the friction coefficient and wear resistance of the specimens were improved by the UNSM technique. The hardness of the specimens also increased after UNSM treatment, but it decreased abruptly with increasing depth from the very top surface. Microscratch tests showed that the critical load of the specimens was improved by the UNSM technique. In addition, Raman spectra results revealed that no additional phase was detected after UNSM treatment, but the intensity decreased after UNSM treatment. Hence, the UNSM technique ensures stronger ceramics and enables better friction and wear behavior than available conventional sintered ceramics.     

Tribological behavior and phase transformation of single-crystal silicon in air

The tribological behaviors and phase transformations of single-crystal silicon against Si₃N₄ with different sliding velocities and durations under low contact stress at room temperature were investigated. SEM and Raman analysis indicate that phase transformation was involved and characterized by plastically deformed area which consists of Si-III, Si-XII, and a-Si, especially in the early stage at the low sliding velocity. The plastically deformed layer was wiped off at high-velocity or long sliding duration. TEM analysis indicated that the wear debris consists of amorphous silicon.     

The Sliding Friction of Hybrid Composite Journal Bearing Under Various Test Conditions

The friction and wear behaviour of SiC, Si₃N₄ and SiC/Si₃N₄ composite ceramics were investigated with oscillating sliding (gross slip fretting) at room temperature. The influence of counter body material and the humidity of the surrounding air was studied with a ball-on-disc configuration with different ball materials (1000Cr6, Al₂O₃ SiC and Si₃N₄). The effect of RH on friction is marginal with exception of SiC (low friction) as counter body material. The wear behaviour, however, is strongly affected by humidity, showing inverse trends for different counter body materials. Consequently, the wear behaviour of a tribo couple can be improved by selecting an adequate mating material. The results reveal the necessity to control RH in tribological tests. For estimation of the performance of tribo couples under varying environmental conditions, a variation of RH is required. In tribo couples with single phase SiC, either as ball or disc, the tribological behaviour of the system is dominated by SiC. The friction behaviour of the composite material is in between the behaviour of the two single phase materials, Si₃N₄ and SiC, whereas the wear behaviour is very similar to that of single phase Si₃N₄.     

Tribological behaviour of uni-directionally aligned silicon nitride against steel

Textured silicon nitride, where the β-Si₃N₄ grains were uni-directionally aligned, was fabricated and the effect of anisotropy in microstructure on tribological properties was investigated, compared with a conventional Si₃N₄. The wear tests were carried out for the tribopair of textured silicon nitride ceramic and steel using a block-on-ring tester without lubrication. For the textured Si₃N₄, tribological properties were evaluated in three directions with respect to the grain alignment; the plane normal to the grain alignment and in the directions parallel and perpendicular to the grain alignment in the side plane. The friction coefficient values of each specimen were of the same level under the same sliding conditions. The values of specific wear rate for the plane normal to the grain alignment were lower than those of the other specimens for all sliding conditions. It is considered that the high wear resistance of this plane was caused by restricted microfracture, such as grain dropping and minimal abrasion by wear debris. Both the friction coefficient and specific wear rate were decreased with increasing sliding speed and normal load because of the formation of lubricative FeO between the sliding surfaces.     

Tribological properties of γ-Y2Si2O7 ceramic against AISI 52100 steel and Si3N4 ceramic counterparts

Reciprocating ball-on-flat dry sliding friction and wear experiments have been conducted on single-phase γ-Y₂Si₂O₇ ceramic flats in contact with AISI 52100 bearing steel and Si₃N₄ ceramic balls at 5–15 N normal loads in an ambient environment. The kinetic friction coefficients of γ-Y₂Si₂O₇ varied in the range over 0.53–0.63 against AISI 52100 steel and between 0.51–0.56 against Si₃N₄ ceramic. We found that wear occurred predominantly during the running-in period and it almost ceased at the steady friction stage. The wear rates of γ-Y₂Si₂O₇ were in the order of 10^?4 mm³/(N m). Besides, wear debris strongly influenced the friction and wear processes. The strong chemical affinity between γ-Y₂Si₂O₇ and AISI 52100 balls led to a thick transfer layer formed on both contact surfaces of the flat and counterpart ball, which changed the direct sliding between the ball and the flat into a shearing within the transfer layer. For the γ-Y₂Si₂O₇/Si₃N₄ pair, a thin silica hydrate lubricant tribofilm presented above the compressed debris entrapped in the worn track and contact ball surface. This transfer layer and the tribofilm separated the sliding couple from direct contact and contributed to the low friction coefficient and wear rate.     

Effect of counterparts on the friction and wear behavior of polyelectrolyte multilayers

Polyelectrolyte multilayers (PEMs) were prepared on Si substrates by alternative deposition of poly(sodium 4-styrenesulfonate) (PSS) as polyanion and poly (diallyldimethylammonium chloride) (PDDA) as polycation. The PEM film was characterized by means of ultraviolet-visible light absorption spectrometry and atomic force microscopy. The friction and wear behavior of the polymer film sliding against brass, 440C stainless steel, Si₃N₄ and WC balls was evaluated on a microtribometer. It was found that the multilayer film was uniform and compact, and it registered a lowered friction coefficient and extended antiwear life while sliding against soft counterparts, in particular, a brass ball. This could be because the polymeric transfer film had an enhanced adhesion on the soft metallic counterpart in the presence of inter-transferred metallic debris. Contrary to the above, the PEM film had a higher friction coefficient and shorter antiwear life while sliding against Si₃N₄ and WC balls, possibly owing to a higher shearing stress in the presence of stiff and hardly deformable hard counterparts. In other words, the polymeric transfer film on the hard couterparts, if any, would be easily scaled off, leading to decreased antiwear life. Moreover, the differences in the friction and wear behavior of the PEM film sliding against different counterparts were closely related to the differences in the chemical and crystallographic structure of the counterparts (ceramics Si₃N₄ and WC, and metals brass and stainless steel).     

Ceramic-ceramic composite materials with improved friction and wear properties

Dry friction and wear tests were performed with self-mated couples of SiC containing 50% TiC, Si₃N₄---BN, SiC---TiB₂ and Si₃N₄ with 32% TiN at room temperature and 400°C or 800°C.Under room temperature conditions, the friction coefficient of the couple SiC---TiC/SiC---TiC is only half of that of the couple SiC/SiC and the wear is one order of magnitude smaller. At 400°C, it exceeds the friction coefficient of SiC/SiC except at the highest sliding velocity of 3 m s⁻¹. At lower sliding velocities the wear coefficient of SiC---TiC/SiC---TiC is lower than that of SiC/SiC.The couple Si₃N₄---TiN/Si₃N₄---TiN exhibits high friction coefficients under all test conditions. At room temperature the wear volume of the self-mated couples of Si₃N₄ and Si₃N₄---TiN after a sliding distance of 1000 m is similar, but Si₃N₄---TiN shows a running-in behaviour. At 800°C the wear coefficient of Si₃N₄---TiN/Si₃N₄---TiN is approximately two orders of magnitude smaller than that of Si₃N₄/Si₃N₄, and equal to those at room temperature. At 22°C the addition of BN reduces the friction of Si₃N₄. The wear coefficient is independent of sliding velocity and the self-mated couples showing running-in. Friction and wear increase with increasing temperature. The wear coefficient of SiC---TiB₂ above 0.5 m s⁻¹ at 400°C is advantageously near 10⁻⁶ mm³ (Nm)⁻¹. With the other test conditions the wear behaviour is similar to SSiC.     

Dry and water-lubricated slip-rolling of Si3N4- and SiC-based ceramics

Tests on self-mated Si₃N₄- and SiC-based ceramics as well as ceramic-ceramic composites were performed in an Amsler-type wear tester under dry and water-lubricated rolling conditions with 10% slip. Under dry friction, wear coefficients of the materials varied by four decades. Unlubricated wear coefficients below 10⁻⁷ mm³/(N.m), defined as a practical limit for applicability, can be achieved with Si₃N₄-TiN below 775 MPa and with HIP-SiC below 750 MPa. HIPped Si₃N₄ and hot-pressed SiC-TiC under dry friction exhibit a small dependency of wear coefficient on Hertzian pressure, with wear coefficients below 10⁻⁶ mm³/(N.m). The lowest wear coefficient below 10⁻⁶ mm³/(N.m) with water lubrication was found for Si₃N₄-TiN and S-RBSi₃N₄; water reduces the variability in wear coefficient for Si₃N₄- and SiC-based ceramics.     

Tribochemical effects on the friction and wear behaviors of diamond-like carbon film under high relative humidity condition

Friction and wear behaviors of diamond-like carbon (DLC) film in humid N₂ (RH-100%) sliding against different counterpart ball (Si₃N₄ ball, Al₂O₃ ball and steel ball) were investigated. It was found that the friction and wear behaviors of DLC film were dependent on the friction-induced tribochemical interactions in the presence of the DLC film, water molecules and counterpart balls. When sliding against Si₃N₄ ball, a tribochemical film that mainly consisted of silica gel was formed on the worn surface due to the oxidation and hydrolysis of the Si₃N₄ ball, and resulted in the lowest friction coefficient and wear rate of the DLC film. The degradation of the DLC film catalyzed by Al₂O₃ ball caused the highest wear rate of DLC film when sliding against Al₂O₃ ball, while the tribochemical reactions between DLC film and steel ball led to the highest friction coefficient when sliding against steel ball.     

Nano Si3N4 composites with improved tribological properties

Nano Si₃N₄ composites with tailored microstructure were developed using fine ß‐Si₃N₄ powders. Their wear behaviour was investigated. Whereas pure Si₃N₄ composites showed improved wear behaviour under dry rolling conditions with slip, TiN‐reinforced nano Si₃N₄ composites generate a self‐lubricating behaviour under dry sliding conditions. After chemical treatment with hydrogen sulphide, the friction coefficient and wear rate was found to be significantly decreased under dry sliding conditions. Additionally, the new composites possess higher fracture toughness than the pure nano Si₃N₄ materials. Copyright © 2009 John Wiley & Sons, Ltd.     

Tribological Properties of Hard Carbon Films on Zirconia Ceramics

In this study, the authors investigated the tribological properties of hard diamondlike carbon (DLC) films on magnesia-partially stabilized zirconia (MgO-PSZ) substrates over a wide range of bads, speeds, temperatures, and counterface materials. The films were 2 μm thick and produced by ion-beam deposition at room temperature. Tribological tests were conducted on a ball-on-disk machine with MgO-PSZ balls, in open air of 30 to 50% relative humidity under contact loads of 1 to 50 N, at sliding velocities of 0.1 to 6 m/s, and at temperatures of 400°C. Al₂O₃ and Si₃N₄ balls were also rubbed against the DLC-coaled MgO-PSZ disks, primarily to assess their friction and wear performance and to compare it with that of MgO-PSZ balls. A series of long-duration lifetime tests was run at speeds of 1, 2, and 6 m/s under a 5 N load to assess the durability of these DLC films. Results showed that the friction coefficients of MgO-PSZ balls sliding against MgO-PSZ disks were 0.5-0.8, and the average specific wear rates of MgO-PSZ balls ranged from 1 × 10^?5 to 5 × 10^?4 mm³/N·m, depending on sliding velocity, contact load, and ambient temperature. The friction coefficients of MgO-PSZ balls sliding against the DLC-coaled MgO-PSZ disks ranged from 0.03 to 0.1. The average specific wear rates of MgO-PSZ, balls were reduced by three to four orders of magnitude when rubbed against the DLC-coaled disks. These DLC films could last 1.5 to 4 million cycles, depending on sliding velocity. Scanning electron microscopy and micro-laser Raman spectroscopy were used to elucidate the microstructural and chemical nature of the DLC films and worn surfaces.     

Friction, wear and N2-lubrication of carbon nitride coatings: a review

Recent results of tribological properties of carbon nitride (CN_x) coatings are reviewed. CN_x coatings of 100 nm thickness were formed on Si-wafer and Si₃N₄ disks by the ion beam mixing method. Friction and wear tests were carried out against Si₃N₄ balls in the environments of vacuum, Ar, N₂, CO₂, O₂ or air by a ball-on-disk tribo-tester in the load range of 80-750 mN and in the velocity range of 4-400 mm/s.It was found that friction coefficient μ is high (μ=0.2-0.4) in air and O₂, and low (μ=0.01-0.1) in N₂, CO₂ and vacuum. The lowest friction coefficient (μ<0.01) was obtained in N₂. It was also found that N₂ gas blown to the sliding surfaces in air effectively reduced the friction coefficient down to μ≈0.017. Wear rate of CN_x coatings varied in the range 10⁻⁹-10⁻⁵ mm³/N m depending on the environment.The wear mechanisms of CN_x in the nanometer scale were studied by abrasive sliding of an AFM diamond pin in air. It was confirmed that the major wear mechanism of CN_x in abrasive friction was low-cycle fatigue which generated thin flaky wear particles of nanometre size.     

Wear and Degradation Characteristics of Perfluoroalkylpolyethers (PFPEs) in High Vacuum©

Wear and degradation as exhibited by degassing of three commercially available perfluoroalkylpolyethers, A, straight chain with acetal linkage (OCF₂CF₂)_p(OCF₂)_q;B, straight chain without acetal linkage (CF₂CF₂CF₂O)_n; C, branched chain (CFCF₃CF₂O)_m, were evaluated at 0.025 mis under 1 to 300 N at 10^?5 Pa in a four-ball configuration using 440C and Si₃N₄ balls, Φ:6.35 mm, as test specimens. A quadrupole mass spectrometer having a mass range of 1 to 200 amu was employed to analyze gaseous products released from the sliding surfaces.

Disregarding the gas released, Oil C showed slightly better wear characteristics than B, but far better than A when tested with a 440C ball on 440C balls.

Taking gas evolution into account, Oil B carried the highest load; the initial degassing was detected at the Hertzian pressure of 1 GPa for A, 2 GPa for B, and 1.75 GPa for C when using 440C balls, and at 1.5 GPa for A and 2.75 GPa for C when using Si₃N₄ balls. Oil B evaluated with Si₃N₄ balls did not evolve gases even at 2.75 GPa. The initial outgassing load of sliding pairs of a Si₃N₄ ball against 440C balls and vice versa was closer to that of a 440C ball on 440C balls than to a Si₃N₄ ball on Si₃N₄ balls.

Mass spectra patterns obtained from experiments with a Si₃N₄ ball on Si₃N₄ balls were similar to those from experiments with a 440C ball on 440C balls.

Oil A released more CFO⁺ (m/e = 47) and CF₂O⁺ (m/e = 66) than Oil B or C, which could originate from the acetal linkage of its molecular structure as shown by Mori and Morales (1).     

Ultra-low friction coefficient in alumina–silicon nitride pair lubricated with water

In a ball-on-disc wear test, an alumina ceramic body sliding against a silicon nitride ceramic body in water achieved an ultra-low friction coefficient (ULFC) of 0.004. The profilometer and EDX measurements indicated that the ULFC regime in this unmated Al₂O₃–Si₃N₄ pair was achieved because of the formation of a flat and smooth interface of nanometric roughness, which favored the hydrodynamic lubrication. The triboreactions formed silicon and aluminum hydroxides which contributed to decrease roughness and shear stress at the contact interface. This behavior enables the development of low energy loss water-based tribological systems using oxide ceramics.     

Surface Engineering Design of Alumina/Molybdenum Fibrous Monolithic Ceramic to Achieve Excellent Lubrication in a High Vacuum Environment

Al₂O₃/Mo fibrous monolithic ceramics are potential candidates for space applications because of their excellent mechanical properties and low density. This study aims at achieving low friction and long life of this material in a high vacuum environment. Three-dimensional composite-lubricating layers were fabricated by considering texture pattern as storage dimples and MoS₂ synthesized via hydrothermal method as lubricant. The tribological properties were studied sliding against Si₃N₄ ceramic and GCr15 bearing steel balls under high vacuum condition. Results showed that the lubricating properties of the Al₂O₃/Mo fibrous monolithic ceramics were improved greatly by the micro-texture and MoS₂ solid lubricant; the friction coefficients were as low as approximately 0.08 and 0.04, respectively, when Si₃N₄ ceramic and GCr15 bearing steel balls acted as the pairing materials. It was also demonstrated that the low friction coefficient can be realized with various normal loads and sliding speeds, indicating the composite-lubricating layers have good adaptation of working conditions. This excellent performance of the material is mainly because of MoS₂ stored in dimples can be easily dragged onto the friction surface to form lubricating and transferring films during the friction process. This work is an extension of studies that were previously published in Tribology Letters journal.     

Effect of counterface balls on the friction layer of Ni3Al matrix composites with 1.5 wt% graphene nanoplatelets

Research on the friction layer is needed to minimize friction- and wear-related mechanical failures in moving mechanical assemblies. Dry sliding tribological tests of Ni₃Al matrix composites (NMCs) with 1.5 wt% graphene nanoplatelets (GNPs) sliding against different counterface balls are undertaken at the condition of 10 N–0.234 m s^?1 in this study. When sliding against GCr15 steel, a uniform and thick friction layer is formed, resulting in a lower friction coefficient (0.29–0.31) and wear rate (2.0–3.1 × 10^?5 mm³ N^?1 m^?1). While sliding against Al₂O₃ and Si₃N₄, the formation and stability of the friction layers are restricted in the severe wear regime, and the NMCs exhibit higher friction coefficients and wear rates. Therefore, various counterface balls have a great effect on the stability and thickness of the friction layer, thus affecting the tribology performance of NMCs. The result also shows that GNPs exhibit enrichment and self-organized microstructures in the friction layer. In addition, the friction layer is also found to be divided into two layers, protecting the subsurface from further damage and reducing shear.